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Pump and adjacent pipes diameter selection - General Question

Hi,

Very new to modelling and selecting upgrades for water supply networks and was just wondering if there is a general rule of thumb on diameter selections for a pump and adjacent pipes on the suction and discharge sides?

If I required a pump to be placed in between 150mm suction and discharge pipework at a small towns WTP, what are the rules for selection of the pump's diameter?

If I was to go a 100mm diameter pump the costs would be less for the initial pump cost and the suction pipework of 150mm may help reduce losses into the pump. If I selected a 150mm diameter pump however, possible reduction in power consumption may occur to discharge the water into the 150mm pipework in comparison to the 100mm pump but added initial costs for the larger pump would be necessary.

If I needed to then upsize to 200mm pipework for the suction and discharge pipework to solve head loss issues, would a 100mm pump diameter still be suitable or would a 200mm pump diameter be preferable?

These are a couple of the issues I'm facing and have little knowledge in the area so was just wondering what others thoughts are for selecting the adjacent pipes diameters on suction and discharge sides of a pump as well as pump diameter selection ?

For most of your questions we would recommend you review the design codes and manuals for your region as those should govern any design and can be regionally very specific. This forum deals mostly with hydraulic modeling rather than pump station design which can be very different in nature and requires specific design calculations and knowledge of the applicable codes to answer.

Generally most pumps have larger suction piping than discharge piping because the designer is concerned about maintaining NPSH requirements on the suction side and available head is limited. Since the pump has added a bunch of energy to the system the discharge pipes are typically smaller than the suction line as these can usually afford to burn a little bit of energy.

For your particular situation you need to first determine your design requirements and perform a detailed analysis to ensure that the changes requested will still allow the pumps to work properly and would help you verify what if any changes would be necessary based on the specific pump requirements and the existing equipment. You can often talk with your pump supplier to find out specific pump requirements, but what you are asking is really part of a specific engineering design analysis which should be done to properly design the station.

You are very welcome. Pump inlet conditions in particular are often very critical to proper pump operation and generally have very specific requirements to ensure the pump works properly. You definitely want to make sure that design is done properly so that your pump works as expected! If done improperly you can get vortices which can could dramatically limit the capacity of the pump. Specific requirements are usually specific for that pump, but the manufacturer often will give inlet flow requirements.

Make sure to have the design checked by a licensed engineer as well to make sure all significant concerns are addressed if this is for an actual pump to be put out to bid and built. Most places require these plans to be stamped by a professional Engineer before it can be built.

Patrick Moore

Originally Posted by StudentEngineer

Hi Patrick,

l'll be sure to get in contact with a pump supplier to assist with the task but appreciate the time to respond. Certainly helped clear it up a little and understand what's needed.